Ammonium nitrate treatment of finely divided coal to reduce swelling and coking



United States Patent O AMMONIUM NITRATE TREATMENT OF FINELY DIVIDED COAL TO REDUCE SWELLING AND COKING Andries Voet and Trevor George Lamond, Borger, Tex., assignors to J. M. Huber Corporation, Locust, N..l., a corporation of New Jersey No Drawing. Filed July 19, 1967, Ser. No. 654,366

Int. Cl. C101) 57/08, 31/08 US. Cl. 2019 1 Claim ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention The invention lies in the field of of the production of activated carbon and more particularly is directed to a method of preparing a material from bituminous coal which is then suitable for activation by conventional methods.

Description of the prior art Activated carbon has been produced by prior art methods from many different kinds of carbonaceous materials such as wood, peat, lignite, nut shells, bones, and vegetable or other carbonaceous matter. Bituminous coal having a B.t.u. content greater than 14,000 units per pound on a moist mineral matter free basis has, previous to the present invention, been generally unsuited for activation since it swells to an undesirable extent when subjected to carbonization in the temperature range from 300 to 700 C. Almost invariably the swelling is accompanied by melting and agglomeration of the coal particles into a plastic mass. On cooling, a coke is formed which is not suitable as a raw material for the production of activated carbon, in view of the coalescence of the originally ground particles.

While it is well known that the swelling and coking properties of coal can be destroyed by oxidation using suitable agents such as air, chlorine, and other gaseous oxidizing materials, such materials are not suitable for the manufacture of active carbon. It is essential that material for activation be in a powdered state with particles of a size preferably below 100 microns. Oxidative treatment of coal powder with gaseous oxidizing agents at elevated temperatures has not been successful, in view of the ease of spontaneous, often explosive ignition of finely divided coal particles upon oxidation. Larger grains of coal do not show this high reactivity but require long periods of treatment to insure penetration of the oxidizing gas into the center of the grain. Such periods of time required are often in excess of 24 hours. In view of these problems met when using finely divided coal particles and the larger grains, the use of oxidizing gases has been economically unattractive. Aqueous oxidizing agents such as KMnO K Cr O NaOCl and the like have been proposed, but these agents leave an undesirable ash in the finished product.

SUMMARY We have discovered that finely powdered bituminous coal may be intimately mixed with aqueous solutions of ammonium nitrate and then heated to produce a powdered material devoid of undesirable swelling and coking properties when subjected to activating conditions. Bituminous coal mentioned in the specification and claims used in practicing the invention refers to a product having a B.t.u. content greater than 14,000 units per pound on a moist mineral matter free basis.

The method of mixing aqueous solutions of ammonium nitrate with ground bituminous coal is not critical. The solution could be added to the powdered coal in a conventional mixer or it could be sprayed on agitated coal particles. The ammonium nitrate could be advantageously dissolved in the water of pelletization mixed with ground coal in a mechanical mixer prior to pelletization. The concentration of the ammonium nitrate in the water used is not at all critical in this process since oxidization starts only at elevated temperatures after substantially all of the water in which the ammonium nitrate has been dissolved is evaporated. The reaction of ammonium nitrate with the volatile components of the bituminous coal to destroy swelling and coking properties starts measurably at about 150 C. and proceeds at a rapid pace at temperatures above 200 C. Temperatures of between 200 and 300 C. give the most useful results. Higher temperatures are not advantageous in this oxidation stage in view of the risk of premature swelling and coking prior to completion of the desirable degree of oxidation.

In the process of oxidation of ground particles of volatile bituminous coal it may be desirable to destroy the swelling properties Without destroying the coking prop erties. Such non-swelling but coking powders are excellent raw materials for the formation of hard pellets of granular activated carbon upon the proper treatment in activation. On the other hand, for powdered activated carbon the more desirable raw material is powdered bituminous coal which has lost both swelling and coking properties. We have observed that quantities of ammonium nitrate of /4 to 3% by weight on the coal destroys the swelling properties without significantly altering the coking properties of powdered bituminous coal upon subsequent heating. Quantities over 3% by weight of ammonium nitrate significantly reduce both swelling and coking characteristics of the coal. Generally, optimum destruction of swelling and coking properties is obtained at a 15% concentration of ammonium nitrate. Larger quantities do not produce a further reduction in swelling and coking qualities.

The time required for the elimination of swelling or swelling and coking properties of the bituminous coal differs somewhat dependent on concentrations, temperature and degree of subdivision of the coal. Generally, however, at least 10 minutes are required for reaction under favorable conditions while reactions are completed under less favorable conditions in less than 12 hours.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of our invention is most advantageously outlined by the following examples.

EXAMPLE 1 1000 grams of a low volatile bituminous coal was ground to permit to pass through a 200 mesh screen. Its volatile matter was 17% (ASTM D720-57), at 14,640 B.t.u./lb. (moist mineral matter free basis) and a free swelling number of 8 (ASTM D980-53). The coal was mixed with 300 grams of a solution containing 25 grams NH NO The mixture was dried for three hours at 210 3 C. in a non-oxidizing atmosphere. This treatment resulted in the formation of a coal without swelling properties, but which had unimpaired coking characteristics. EXAMPLE 2 Example 1 was repeated except that the solution contained 80 grams of NH NO The treatment resulted in the formation of a coal without swelling properties and with a partial loss of coking properties.

EXAMPLE 3 Example 1 was repeated except that a medium volatile bituminous coal was used with a 29% volatile matter content, at 14,230 B.t.u./lb. (moist mineral matter free basis) and a free swelling number of 6.5. The mixture was dried at 240 C. in a non-oxidizing atmosphere, resulting in a product Without swelling properties but with unimpaired coking properties.

EXAMPLE 4 Example 3 was repeated except that 90 grams of NH NO was used, resulting in a produce without swelling properties and with greatly reduced coking properties.

EXAMPLE 5 1000 grams of a high volatile bituminous coal, with 38.8% volatile matter, at 14,170 B.t.u./lb. (moist mineral matter free basis) and a free swelling number of 8 was ground to permit 85% to pass through a 200 mesh screen. The coal powder was pelletized in a pin mixer with a solution of 2.5 grams of NH NO in 300 grams of water. The pellets were dried for 3 hours at 250 C. in a non-oxidizing atmosphere.

EXAMPLE 6 Example 5 was repeated using successively greater quantities of NH NO with the results illustrated in Table I below.

tion. Thus a treatment of the finer fraction with 6% NH NO was equivalent to a treatment of the coarser fraction with 7.8% NH NO by weight on the coal.

Coarser fractions than 35 mesh, which have an average diameter in excess of 0.5 mm., require a longer period of time and a higher concentration of NH NO to result in a significant reduction or elimination of swelling properties. The use of such coarser fractions, therefore, is not suitable to produce an economic product in the practice of the present invention.

Nonoxidizing atmosphere as used herein refers to an atmosphere so low in oxygen content that it will not support combustion of the coal.

It should be understood that the ammonium nitrate and water comprising the aqueous solution may be added to the coal particles separately without in any way changing the final result.

We claim:

1. A method of producing a powdered coal product having reduced swelling properties and suitable for activation to produce activated carbon, said method comprising the steps of:

(a) mixing a bituminous coal having a grain size not greater than 0.5 mm. and a B.t.u. content, on a moist mineral free basis, greater than about 14,000 units per pound, with an aqueous solution of ammonium nitrate having an ammonium nitrate content in the range of from 3.0 to 15 parts by weight per 100 parts by weight of said bituminous coal,

(b) heating the mixture to from 150 C. to 300 C. for from 10 minutes to 12 hours in a non-oxidizing atmosphere, and

(c) recovering a powdered coal product having reduced swelling and coking properties.

TABLE I.-PROPERTIES OF OXIDIZED COAL NH4NO grams 2.5 15 30 60 80 120. Swelling properties... Reduced Greatly d Destr0yed Destroyed. Destroyed Destroyed.

re 1109 Coking properties Unchanged Unchanged".-. Uncl1anged..-- Reduced G r eg t l y Do.

EXAMPLE 7 References Cited FOREIGN PATENTS 405,312 10/ 1924 Germany.

PATRICK P. GARVIN, Primary Examiner P. E. KONOPKA, Assistant Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3 ,536,589 D ted October 27, I970 Inv n fls) Andries Voet and Trevor George Lamond It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

At coI umn I I ine 29, deI ete one of the dupI icated words "of" immediateIy foIIowing the word "fieId;

At coIumn 3, I ine 6, deIete "NH N and substitute NH N0 At coIumn 3, Iine 20, deIete "produce" and substitute product At coIumn 3, Iine 38, (in TABLE I deIete "NH N0" and substitute NH N0 CoIumn 3, I ine 38 shouId appear as foI Iows:

TABLE I PROPERTIES OF OXIDIZED COAL NH N0 grams 2.5 I5 I20 mum S9150 w w 51- FEB 231971 I Attest: g?

nmuu E. soEuYmR, m

. Offioer commissioner of Patents FORM PO-IOSO (10-69) uscoMM-Dc 60376-P69 U 5, GO UINMENY PRINTING OFFICE: "I! 0Ji-JJ4 

